Topic 14: Ultrasound imaging
Physics Objectives category 1 • Demonstrate knowledge of the basic physical nature of ultrasound waves and the interactions that occur as it traverses through tissues and other media. • Demonstrate knowledge of the various types of ultrasound transducers which are available, and to be able to choose a transducer on the basis of its physical characteristics and suitability for a given application. • Demonstrate knowledge of the basic principles of ultrasound imaging and how various technical factors affect image quality. • Describe how real-time systems work, and be aware of the interplay between temporal resolution, spatial resolution and depth of penetration. • Describe the basic physical principles underlying the use of the Doppler effect in ultrasound imaging. Explain how choice of frequency affects attenuation, spatial resolution, and the maximum flow rate that can be detected. • Describe the operation of a simple duplex transducer. • Recognise simple ultrasound artefacts and explain how they are formed. • Discuss the main mechanisms by which ultrasound could damage tissue. Have a knowledge of safe levels of exposure for imaging and safety recommendations. Topics category 1 (a) Fundamental physics of ultrasound and interaction with tissues: • Interference, diffraction, resonance • Reflection, refraction • Attenuation, absorption, scattering (b) Transducers and the ultrasonic field: • Piezoelectric effect • Linear & convex arrays • Phased arrays c) Pulse-echo imaging and instrumentation: • Grey-scale imaging • Receiver functions: – Time-gain compensation (TGC) • Digital processing: – Pre- & post-processing • Spatial resolution (d) Real-time systems • Basic principles (e) Doppler systems: • Doppler effect & Doppler shift equation: – Basic principles – Limitations on velocity measurement (f) Ultrasound artefacts: • Multiple reflections – reverberation • Attenuation: – Shadowing – Enhancement (g) Biological effects: • Mechanisms of interaction with tissues • Thermal and mechanical incices • Safety recommendations • Australasian Society for Ultrasound Medicine (ASUM) Safety Statements Objectives category 2 • Demonstrate knowledge of some of the basic parameters which characterise a sound wave. Conduct simple calculations relating to frequency, wavelength and relative intensity in decibels. Demonstrate working knowledge of the relative magnitudes of sound velocity, acoustic impedance and attenuation in various biological media, and their implications for imaging. • Describe details of the main physical parameters that characterise transducers, and their effect on the image. • Describe the basic principles of B-mode pulse-echo imaging. Understand parameters such as pulse length, frequency, pulse repetition frequency and TGC affect the image. • Perform simple calculations using the Doppler shift equation and understand the concepts underlying spectral analysis colour Doppler and power Doppler. • Describe the basic principles of compound imaging. • Describe the basic principles of panoramic imaging. • Explain the factors which produce more complex artefacts such as aliasing and side lobes. Topics category 2 (a) Fundamental physics of ultrasound and interaction with tissues: • Wave motion and types of waves • Wave length, frequency, phase • Intensity, pressure, amplitude • Decibel notation - intensity and amplitude • Velocity in liquids and biological media • Acoustic impedance (b) Transducers and the ultrasonic field: • Beam pattern - near & far field • Focused transducers - types & techniques • Broad bandwidth transducers c) Pulse-echo imaging and instrumentation: • B-mode (d) Doppler systems: • Doppler effect & Doppler shift equation: – Direction detection – Spectral analysis • Colour and power Doppler (e) Compound imaging (f) Panoramic imaging (g) Ultrasound artefacts: • Beam width - side lobes • Instrumentation artefacts (colour Doppler aliasing) Objectives category 3 • Demonstrate a working (although not necessarily detailed) knowledge of more complex technology involving: • Special transducers • Harmonic imaging, 3D imaging and ultrasound contrast agents. Topics category 3 (a) Transducers and the ultrasonic field: • Special types of transducer: – Intracavity probes – Biopsy and surgical probes • A-mode (b) New techniques: • Harmonic imaging • Contrast agents • 3D/4D imaging with ultrasound © Ultrasound artefacts: • Refraction - sound speed errors